var reverseList = function (head) {
  //pre指针：上一节点 current指针：当前节点
  let pre = null
  current = head
  //只要当前节点不为空
  while (current) {
    //临时指针：暂存当前节点的下一节点
    let temp = current.next
    //current指针的next指向pre
    current.next = pre
    //pre指针和current指针都指向下一节点
    pre = current
    current = temp
  }
  //返回pre指针
  return pre
};